The present invention relates to bone-fixing devices which may be utilized to maintain plurality of bones in a specified positional relationship by installing a pedicle in each of the bones and employing a fixture to fix said pedicle to a reference shaft to position the bones.
A bone-fixing device of this type has various uses, such as disposing a reference shaft substantially in parallel with the spine and employing a fixture to fix a pedicle implanted in the vertebra thereof to said shaft. Although great care is exercised in implanting the pedicle in each vertebra, it is impossible to locate all the pedicles in the same direction,and in order to absorb the differences created, there is provided some range of adjustment at the junctions between the pedicle and the fixture, as well as between the fixture and the rod shaft.
An example of a bone-fixing device is disclosed by Japanese Patent Application laid-open No. 255739/95, in which a flange to be assembled in a pedicle and a member known as a lock pin are employed to achieve a construction in which some parts can be moved in two directions which perpendicularly intersect with each other. The distance between the pedicle and the shaft can be adjusted in the necessary range of adjustment by constructing a connecting means that can move to a suitable position along the bar of said connecting means. In the prior art device, according to that invention, it is necessary to carry out certain steps such as inserting the flange into the head of a screw to be threaded into the bone, inserting the lock pin into said head to fix the flange, putting the assembly into a connecting means and then inserting the connecting means into the bar to tighten it with a screw.
It is very troublesome, however, to require the foregoing complicated steps to assemble the above-mentioned parts into such a device and to adjust the position relationship between them. It is also difficult to reassemble these parts as necessary once they have temporarily been assembled. In addition, the device is designed so that the retaining screw is threaded into the bar in order to tighten the head of the bone screw which comes directly below said retaining screw, thus requiring the upper part of the bone screw to be open. This means that a wider incision range will be necessary to set the device, resulting in a prolonged operation time and curing period.